The primary objective of this pilot study is to determine whether the presence of Actinobacillus actinomycetemcomitans (Aa), a Virulent" clone of Aa (the JP2 clone), or specific microbial complexes could be predictive of the initiation and progression of Localized Aggressive Periodontitis (LAP) in periodontally healthy African-American and Hispanic children, two populations with a high prevalence of LAP. The first aim will be to investigate the relationship between the presence of Aa in healthy children and subsequent disease initiation. The second aim will be to determine whether the presence of specific virulent clones of Aa will initiate conversion from health to disease in those children. The third aim will be to determine whether specific pathogenic microbial complexes are associated with disease in the two study populations (crosssectional study) and, if so, whether these "pathogenic complexes" are related to disease initiation (prospective study). 1,200 students, ages 11-14, from Newark will receive a baseline periodontal exam. Bacteria will be collected from each student for identification of Aa by cultural methods and 40 other plaque bacteria by DNA/DNA checkerboard hybridization. 240 Aa culture positive periodontally healthy students and 240 Aa negative matched controls will be selected for the prospective study and examined and sampled every 6 months for two-years. Disease initiation will be detected by increased probing attachment levels and radiographic evidence of bone loss. Statistical analysis will determine whether there is a relationship between students who harbor the target microorganisms (Aa, clones of Aa, or specific microbial complexes) and disease initiation and will be used to determine the design of the proposed follow-up clinical trial: The long-term goal of this proposal is to use the pilot data generated to plan for a definitive clinical trial intended to design strategies for early identification of children at risk for LAP so that cost effective preventive interventions can be developed to significantly reduce the burden of disease in this underserved population. [unreadable] [unreadable]